FIG. 9 shows a conventional gas shutoff apparatus of the above type as disclosed in, for example, JP-A-56-160520.
Referring to FIG. 9, a reference numeral 1 denotes a pipe, in which a shutoff valve 3 for shutting off or passing use gases in the pipe is installed near a gas supply source 2. A reference numeral 4 denotes gas exhaust equipment such as a gas stove, in which an equipment plug 5 is installed. A reference numeral 6 denotes a main controller, which transmits a control signal to the shutoff valve. A reference numeral 7 denotes a pressure sensor unit, which is installed in downstream of the shutoff valve 3. A reference numeral 8 denotes an equipment plug open/close detection unit, which outputs an equipment plug open/close signal in association with open/close operations of the equipment plug 5. A reference numeral 9 denotes a use gas pressure monitoring circuit, and a reference numeral 10 denotes a residual gas pressure detection circuit. When the equipment plug open/close signal is output from the equipment plug open/close detection unit 8, and the gas pressure is detected by the pressure sensor unit 7, the detected gas pressure is output to the use gas pressure monitoring circuit 9 and the residual gas pressure detection circuit 10. A reference numeral 11 denotes a storing circuit, which stores the gas pressure signal from the use gas pressure detection circuit 9 and the residual gas pressure detection circuit 10. A reference signal 12 denotes a shutoff valve open/close circuit, which receives a reduction condition and outputs a blockage signal to the shutoff valve 14 when a pressure reduction signal is input from the use gas pressure detection circuit 9 and the residual gas pressure detection circuit 10 to the storing circuit 11. A reference numeral 13 denotes a return button, and a reference numeral 14 denotes a timer circuit. A reference numeral 15 denotes a safety return circuit, which transmits an output signal from the storing circuit 11 and the timer circuit 12 to the storing circuit 11, the timer circuit 12, and a lamp buzzer circuit 16 when the output signal from the storing circuit 11 and the timer circuit 12 is received, in order to retain a checking condition.
Subsequently, operations of the conventional example will be explained. When the equipment plug 5 of the gas combustion equipment 4 such as a gas stove is opened, an equipment plug open/close signal is output from the equipment plug open/close detection unit 8 to the use gas pressure monitoring circuit 9 and the residual gas pressure detection circuit 10. In addition, the gas pressure detection signal from the pressure detection unit 7 is input to the use gas pressure monitoring circuit 9 and the residual gas pressure detection circuit 10. The use gas pressure monitoring circuit 9 outputs the gas pressure detection signal and the equipment plug open/close signal, which have been input, to the storing circuit 11. When the equipment plug is opened on the basis of these signals, the gas is output to the shutoff valve open/close circuit 12. When the pressure is abruptly reduced below a predetermined value in the case of hose disconnection or the like, the output stops. The input signals such as the equipment plug open/close signal and the gas pressure detection signal to the residual gas pressure detection circuit 10 are output to storing circuit 11 in order to detect an abnormal condition. On the other hand, the output signal from the equipment plug open/close unit 8 is output to each circuit, and the residual gas detection circuit 10 is set when the equipment plug 5 is closed. The residual gas pressure detection circuit 10 starts to detect the residual gas pressure when the equipment plug 5 is closed. When the gas pressure is reduced below a certain value, the storing circuit 11 and the safety return circuit 15 transmits signals to the shutoff valve open/close circuit 12 and the timer circuit 14 to start the timer as well as set the shutoff valve 3 to an open state. Then, it is monitored again whether or not the residual gas pressure is reduced below a certain value within a certain time limit (e.g., within five to fifteen minutes) set by the timer circuit 14. When the gas pressure is reduced below a certain value, a signal is transmitted to the storing circuit 11 and the shutoff valve 3 is locked through the shutoff valve open/close circuit 12. When the gas pressure is not reduced, the storing circuit 11 is reset. The storing circuit 11 stores a gas pressure reduction signal from the use gas pressure monitoring circuit 9 or the residual gas pressure detection circuit 10, and outputs it to the shutoff valve open/close circuit 12 to close the shutoff valve 3. Simultaneously, the signal from the use gas pressure monitoring circuit 9 is output to the lamp buzzer circuit 16 through the timer circuit 14 and the safety return circuit 15 in order to operate a buzzer or an alarming lamp. The shutoff valve open/close circuit 12 receives a signal from the storing circuit 11, which has received the signal from the residual gas pressure detection circuit 10, to stop electric transmission to the shutoff valve 3 in the case of an abnormal signal. The timer circuit 14 is operated on the basis of operation of the storing circuit 11, the safety return circuit 15, or the return button 13, and transmits its output to the lamp buzzer circuit 16 and the safety return circuit 5. The safety return circuit 15 receives the outputs from the storing circuit 11 and the timer circuit 14, and transmits a signal to the lamp buzzer circuit 16, to retain a checking condition. It is noted that, as a method of identifying return safety, when the return button 13 is operated, the shutoff valve 3 is opened, gases are filled in the pipe, and then, the shutoff valve 3 is closed. After that, it is monitored whether a residual gas pressure is reduced within a certain time limit (e.g., about five to fifteen minutes). During that time, a lamp is repeatedly turned on and off to notify a checking condition. In this case, when the gas pressure is not reduced, a normal operation can be performed after completing the check. When the use gas pressure is reduced below a certain value, the shutoff valve 3 is closed, and a lamp is repeatedly turned on and off, or a buzzer rings. In other words, since the shutoff valve 3 is not opened, the gas cannot be used.
[Patent Document 1] JP-A-56-160520